The invention relates to a device for the interferometric measuring of an object as well as a method for the interferometric measuring of an object and a use of a device for the interferometric measuring of an object.
Devices for the interferometric measuring of an object comprise typically a radiation source for generating an output beam, an optic interferometer, as well as a defector. The interferometer is arranged in the radiation path of the output beam and an interference beam is generated by the interferometer, with the detector being arranged in the radiation path of the interference beam.
By evaluating the measuring signal of the detector, for example a conclusion can be drawn about a speed of motion of the surface of the object to be measured. In particular when such a device is embodied for the measuring of the oscillation speed and/or the time-dependent speed and/or path signal of an object this is commonly called a vibrometer.
In such devices it is essential that the Doppler-effect is utilized: The output beam is guided to the object and the beam, at least partially reflected or redistributed, shows a frequency shift based on the motion of the object, which forms the Doppler-effect.
By forming interference and receiving interference signals via the detector the above-mentioned frequency shift is transferred into a frequency range, which can be measured with sufficient precision by optic detectors, such as photodetectors.
Typical devices of prior art for the interferometric measuring of an object comprise an interferometer, which is generally designed based on the two-beam principle. For example, the interferometer may be designed as a Michelson-interferometer, frequently however a Mach-Zehnder-interferometer is realized: The output beam is split via a beam splitter into a measuring beam and a reference beam. The measuring beam is guided to the object and the measuring beam, at least partially reflected or disbursed, is at least partially coupled back into the radiation path of the interferometer and interfered together with the reference beam on the detector, so that in this case the measuring beam and the reference beam, interfered on the detector, represent the interference beam, which its interference signal being measured by the detector.
The above-mentioned devices for the interferometric measurement of an object are also used, in addition to determining the speed of motion, also to determine the direction of motion of the object (typically in a heterodyne embodiment). It is also known to embody the devices as scanning devices, so that respective measurement data is provided for a plurality of measuring points on the object and thus, for example, also data regarding the topography of the object can be determined.
The maximally achievable precision of measurement of such devices, for example the minimally achievable amplitude resolution, is limited by the shot signal noise current, among other things. In devices for the interferometric measurement of an object, with its precision being at or near the limit set thereby, is also called shot signal noise—limited light detection.